Surprisingly, this isn’t a big headline today, but certainly big news.  Fannie Mae and Freddie Mac are seeing huge drops today: [Thanks John for catching this one!]

NEW YORK (CNNMoney.com) — Shares of mortgage financing giants Fannie Mae and Freddie Mac both plunged Monday as fears deepened about the credit crisis and housing meltdown.

In midday trading, shares of Fannie Mae (FNM, Fortune 500) were down 20% and Freddie Mac (FRE, Fortune 500) shares were down more than 22%.

Fannie Mae and Freddie Mac are government sponsored enterprises that help the mortgage market function by purchasing pools of loans and packaging them into securities.

With more than a million Americans facing foreclosure and home prices sinking, the two companies have been hit hard.

The companies bought securities backed by risky subprime mortgages when the housing market was booming, but as the housing market has buckled under credit crisis pressures, concerns have grown about their need for more capital. Some analysts have even suggested that a government bailout of the two may be necessary.

Both stocks are off their session lows currently, but still down big on the day.  To give you an idea of how these stocks have been faring recently, here’s the five-year FNM chart from Yahoo:

Problems with FNM and FRE could have serious implications for the broader housing market:

The collapse of the housing bubble has left them [FNM and FRE] the dominant players in housing finance. Together, they bought the equivalent of 68 percent of the single-family mortgages that originated during the first three months of this year, according to the Office of Federal Housing Enterprise Oversight.

After years of hand-wringing about the risks that Fannie Mae and Freddie Mac’s rapid growth might pose to the financial system, the government has loosened restraints on the companies in the stated hope that they will help prop up the housing market.

It was a strange hope. Toxic portfolios have damaged old and venerable institutions- it was unlikely that the GSEs would be immune to the same poison.